Heater boxes are typically used to supply heated air to an oven to bake a product, such as paint on a vehicle body or other coated substrates. In a typical application, air is directed under pressure by a fan or blower to a burner and the heated air is then directed from the burner to a heater box. The burner mixes fuel, typically natural gas, with air and uses an ignition source to cause combustion and generate heat. Heated air is then generally directed from the burner to a heater box which is typically formed of insulated sheet metal. A circulation fan is generally used to circulate air through the heater box into an oven.
In a typical application, a centrifugal style air blower is used to supply combustion air to the burner. The movement of air through the inlet of such blowers creates a high sound level in the immediate vicinity of the heater box. Typically, the sound levels exceed those deemed safe for human exposure by the Occupational and Safety Health Administration (OSHA). However, sound silencers are commercially available which generally bolt onto the inlet of the blower. These sound silencers are stated to be capable of reducing or attenuating the sound levels by approximately 10 dB. However, one problem with commercially available sound silencers is their relatively large size. Typically, space is limited around the inlet of the combustion air blower, making installation of the sound silencer difficult, if not impossible. Further, commercially available sound silencers are relatively complex and therefore relatively expensive. A conventional sound silencer for this application generally includes a cylindrical housing having a pleated filter and a tubular duct or pipe directs air into the combustion blower. The open end of the cylindrical housing is the air inlet. Air is then received into the cylindrical housing through an annular opening surrounding the tubular duct or pipe and circulated through the air duct to the blower. Typically, the overall length of commercial sound silencers is twenty inches or greater.
As set forth above, however, space is limited around the inlet of the combustion air blower in a typical application. There is, therefore, a need for a noise silencer of this type which is more compact having the same or improved sound attenuation. It would also be desirable, particularly in retrofit applications, to have an improved noise silencer which clamps onto a standard air blower inlet filter using existing clamps. The noise silencer of this invention achieves these advantages.